Control system



Feb. 11, 1941.

J. L. HARRIS CONTROL SYSTEM Filed March 15, 1959 2 sheets-sheet 1 J. L. HARRIS CONTROL SYSTEM Feb. 11, 1941;

2 Sheets-Sheet 2 Filed March 15, 1939 coNosNsEa ,'wentor MMM TRANSFORMER Patented Feb. 11, 1941 PATENT oi-FICE CONTROL SYSTEM John L. Harris, Minneapolis, Minn., assignor to Minneapolis-Honeywell Regulator Com any, Minneapolis, Minn., a corporation of De ware `Application March 15, 1939, Serial No. 261,950

2l Claims.

'This invention relates in general to automatic controls forI multiple unit power installations and more particularly w control of systems utilizing a plurality of ,internal combustion engines and to air conditioning systems of the type employing a plurality of variable speed compressors.

In air conditioning and refrigeration practice, it has become usual to drive compressors by means of internal combustion engines which have the advantage of low cost operation and exibility of output. For larger installations, it has been proposed to utilize a number of enginecompressor units and to control the engines in a manner to vary the speed of one engine from a minimum to a maximum, then to start a second engine and lncreaseits speed from a minimum to a maximum. An arrangement of this type is shown in the copending application of William L. McGrath, Serial No. 218,577 led July gu 11, 1938. This type of arrangement while being generally satisfactory and providing for extreme flexibility in output control however is subject to certain disadvantages which it is the object of the present invention to avoid..

With the type of output control heretofore proposed, in obtaining a system output which is slightly above the output of a single unit, one unit is caused to operate at 'substantially full speed while a second unit operates at low speed. This type of operation causes the second unit to operate ineiiiciently, and with certain types I of prime movers will cause the first unit to operate substantially below maximum efiiciency also. In addition, this type of control causes 3,; the Wear and tear of the units to be very different, also, due to the compressors operating at diierent speeds, the compressor operating at the .higher speed has a lower inlet pressure than the compressor operating at the lower speed 40 which presents dimculties in maintaining the grankcase oil levels in the various compressors uniform.

It is an object of the present invention to provide a control system for multiple unit power t installations which varies both Athe capacity of units inl operation and the number of units in operation, and which also acts to cause operation of the units at equal speeds or capacity.

Another objectof this invention is the pro- ;,0 vision of a multiple unit power installation utilizing internal combustion engines with 'a control system .which acts upcrrv increase in load to increase the speedof one engine from a minimum to a maximum, then to place a second engine in 5,7, operation, and to reduce the speed of the first engine so that the two engines operate at substantially the same speed. A further object of this invention is the provision of an internal combustion control system which places the engine into and out of opera- 1 tion and which locks the engine in operation for a predetermined period after starting to thereby prevent any surges in the power system of which the engine forms a part from causing the engine to stop. m

While the invention is particularly applicable for the controlling of multiple unit internal combustion engine air conditioning or refrigeration systems, its utility is not limited to systems of this type. Other objects of this invention will 15 lindicates an air conditioning chamber which maybe connected by a return duct 2 to the space being conditioned. This chamber is also con- 30 nected to a fan 3 which in turn is connected to the conditioned space by `a discharge duct 4.

, Located within the chamber i is a direct expansion`cooling coil 5. l

Connected to the cooling coil 5 are com- 35 pressors 6, 1, and 8, these compressors having their discharges connected to a' common disf charge main 9 which conveys the compressed refrigerant to a condenser I0. This condenser is .in turn connected by a. liquid line ii to a ther- 40 mostatic` expansion valve i2 which is located at the inlet of cooling coil 5 and which is provided with a control bulb I3 attached to the outlet of this cooling coil. This outlet is connected by a suction line i4 which is in turn connected to the 45 compressors 6, 1, and 8 by pipes i5, i6, and I'l.v

The compressor Bvis driven by means of an `internal combustion engine i8. This engine may be of my desired type such as a gasoline or Diesel engine and for illustrative purposes is indicated as having an intake manifold i9 which is provided with a gaseous fuel line 20 having located therein a throttle valve 2l. This throttle valve is positioned through a suitable linkage 22 by a proportioning type electric motor 55 23. The engine I8 is also provided with a starting motor 24, a generator 25, and an automatic starting relay 26. This relay may be of any desired type, for example, such as shown in the L. K. Loehr' et al. Patent No. 1,773,913. This relay is adapted to be controlled by control wires 21 and 28 which are connected to an auxiliary switch 29 actuated by the proportioning motor 23. This auxiliary switch is arranged so as to close when the` throttle valve 2| is opened beyond a predetermined minimum position by the proportioning motor 23. Closure of this mercury switch 29 energizes the ignition coil 29a ,and also causes energization of the starting relay 26 which operates the starting motor 24 for starting the engine. 'I'his relay 26 also automatically deenergizesthe starting motor 24 when the engine starts and maintains this starting motor deenergized so long as the engine continues to run. When the auxiliary switch 29 is opened due to closure of the throttle valve 2| by motor 23, the energizing circuit for relay 26 is broken and the ignition circuitis also broken for placing the engine I 8 out of operation.

The compressor 1 is-driven by means of an internal combustion engine 38 which is the same as engine I8. This engine is provided with an automatic starting relay 3| controlled by an auxiliary switch 32 which is actuated by the proportioning motor 33 which also actuates the engine throttle valve 34. The switch 32 alsocontrols the energization of the ignition coil for this engine. The compressor 8 is driven by an internal combustion engine 35 having a throttle valve 36 which is positioned, by means of a proportioning motor 31. This engine is also provided with an automatic starting relay 38 which is controlled by means of an auxiliary switch 39 actuated by the proportioning motor 31, this auxiliary switch also controlling the ignition circuit.

Reference character 48 indicates a thermostat for controlling the engine speed. This thermostat is of the potentiometer type and may include a bellows 4I which is connected by capillary tube 42 to a control bulb 43 located within the return air duct 2. The bellows 4| may actuate a bell crank lever having an actuating arm 44 and a control arm or slider 45 which cooperates with a resistance 46 to form a control potentiometer. It will be apparent that upon increase in return air temperature the bellows 4I will expand for rotating the slider 45 to the left across the resistance 46 against the action of a biasing spring 41. Upon decrease in return air' temperature the bellows 4I will contract under the action of the spring 41 for rotating the slider 45 to the right. This instrument may be so designed and adjusted that the slider 45 engages the righthand end of resistance 46 when the return air temperature is at 75 F. or below while .engaging the left-hand end of this resistance when the temperaturerises to 80 F;

The thermostat 48 controls a step controller e generally indicated as 58, this step controller comprising a proportioning motor 5I having an -operating shaft 52 which actuates sliders 53, 54, and 55. The slider 53 cooperates with a resistance 56 while the slider 54 cooperates with a resistance 51 and contact strip 58, andthe slider 55 cooperateswith a resistance 59 and a contact strip 68. By this arrangement, as the sliders 53, 54, and 55 are shifted from their extreme lefthand positions, the slider 53 Will wipe the left- `hand end of resistance 56 while sliders 54 and 55 will wipe the contact strips 58 and 68 respectiveto the right the slider 54 will engage the resistgagement with the contact strip 68. Upon still further movement of the sliders the slider 55 will nally engage the resistance 59. The sliders 53, 54, and 55 therefore sequentially engage their respective resistances.

The motor 5I of the step controller 58 may be of any desired type but is preferably of the type shown and described in the Taylor Patent 2,028,110. Upon reference to this patent it will be found that motor 5| is of the reversible type and is provided with three control terminals which are marked R, B, and W. This motor is adapted to assume various angular positions of its operating shaft in accordance with the relationship between resistance which is connected between terminals R and B and between terminals R and W. 'I'hus if equal values of resistance are connected between these terminals the shaft 52 will assume its intermediate angular position in which the slider 53 engages the center of resistance 56.' However, if the resistance between terminals R and B is increasediwhle the resistance between terminals R and W is decreased, the motor Will-rotate its shaft 42 in a direction for moving the sliders to the left. Conversely if the resistance between terminals R and B is decreased without corresponding decrease in resistance between terminals R and W, the shaft 52 will rotate the sliders 53, 54, and 55y to the right an amount proportionate to the change in resistance. Terminal R or motor 5I is connected to the slider 45 of thermostat 48 by wire 6| while terminal B is connected to the left-hand end of resistance 46 by wire 62 and terminal W is connected to the right-hand end of this resistance by the wire 63. The return air thermostat 48 is therefore in control of the step controller proportioning motor 5I and therefore positions the sliders 53, 54 and 55 in accordance with the return air temperature. Thus as-the return air temperature increases the thermostat 48 will c ause operation of the motor 5I for shifting the sliders 53, 54, and 55 to ther-ight an amount proportionate to the increase 'in return air temperature.

The throttle valve proportioning motorsf23, 33, and 31 are of the same type as the proportioning motor 5I, each of these motors having terminals marked R, W, and B. Terminal R of proportioning motor 23 is connected by means of wire 65 to `-the slider 53 while terminal W is connected by wire 66 to the left-hand end of resistance 56, and terminal B is connected by wire 61 to the righthand end of resistance 56. It should now be apparent that when the space temperature increases, the thermostat 48 will cause rotation of the shaft 52 of proportioning motor 5| which will cause movement of the slider 53 to the right across resistance 56 thereby decreasing the amount of resistance between terminals R and B of motor 23 while increasing'the amount of resistance between-terminals R and W. This will cause the proportioning motor 23 to open the throttle valve 2| an amount proportionate to the rise in return air temperature.

ly. Upon continued movement of these slidersv ance 51 while the slider 55 will still remain in en- Terminal R of proportioning motor 33 is con- I nected to the contact strip 68 by wire 13. The thermostat 40 therefore controls the throttle valve proportioning motors 23, 33 and 31, but due to the sequence control arrangement of the step controller 59 these motors' are controlled in sequence.

Connected `into the control circuit of the proportioning motor 23 is a manually operated potentiometer 15, this potentiometer having a slider 16 and a resistance 11. The right-hand end of resistance 11 is connected to wire liliV by wire 18 and the left-hand end of this resistance is connected to wire 61 by wire 19. The slider 16 is connected by wire 80 to a mercury switch 8| of a pressure responsive device 82 and this mercury switch is connected by wire 83 to the wire 65. It will be apparent that when mercury switch 8| is closed, the potentiometer 15 is connected into the control circuit of motor 23 in parallel with the step controller potentiometer formed of slider 53 and resistance 56. However, when mercury switch 8| is open the slider 16 is disconnected from the control circuit and thus lts position on resistance 11 has no effect upon the motor 23. The pressure responsive device 82 includes a bellows 84 which actuates the mercury switch 8|, this bellows being connected by a tube 85 to the intake manifold of the engine 30. When the engine 39 is out of operation, the mani- .fold pressure will be atmospheric, which will permit the bellows 84 to expand and thus open lmercury switch 8| for disconnecting the potentiometer 15 from the control circuit of motor 23. However, when engine 39 is in operation, a vacuum will occur in the intake manifold thereby contracting Ythe bellows 84 and closing the mercury switch 8l.

Also connected to the control circuit of motor 23 is a manual potentiometer 81 having a. slider 88 cooperating with a resistance 89, the righthand end of this resistance being connected to wire 66 by wire 90 and the left-hand end thereof being connected to wire 61 by wire 9|. The slider 88 is connected by wire 92 to a mercury switch 93 forming part of a pressure responsive device 94. This mercury switch is in turn connected by wire 95 to the wire 65 of the motor control circuit. The pressure responsive device 94 responds to the intake manifold pressure of the engine 35 and includes a. bellows 96 which is connected to this manifold by a. tube 91. f This bellows actuates the mercury switch 93 and valso actuates a second mercury switch 98. When the engine 35 is at rest both of these mercury switches will be open as shown, while when the engine 35 is operating the vacuum produced in the intake manifold thereof will contract the bellows 96 for causing the mercury switches 93 and 98 to close. The mercury switch 98 is provided for the purpose of placing a potentiometer 99 into and out of control relationship with the throttle valve motor 33 of engine 38. This switch is connected by wire |86 to the Wire 68 and is connected to the slider 19| of potentiometer 99 by wire |62. The right-hand end of resistance |03` when the slider 53 moves to the right one-third of the way across resistance 56 the throttle valve 2| will be wide open. This arrangement therefore permits the speed of engine 18 to be increased to a maximum before the slider 54 begins traversing the resistance 51. Therefore engine |8 may operate at full speed even when the engines 3U and 35 are at rest. 'Ihe throttle valve motor 33 is adjusted so that it moves the throttle valve 34 from a position corresponding to one-half capacity to full capacity for a movement of slider 54 4over but half of resistance 51. Consequently when the slider 54 engages the center of resistance 51 the engine 30 may operate at full speed even though the slider 55 is engaging the left-hand end of resistance 59 for causing the throttle valve 36 of motor 35 to be closed suiciently for opening the auxiliary switch 32. 'I'he purpose of the potentiometers 15, 81 and 99 and the controllers 82 and 94 will become apparent from the following statement of v operation.

Operation of Figure 1 Assuming that the space temperature is below '15 F., the slider 45 of thermostat 48 will engage the right-hand end of resistance 46 which causes the step controller motor to position the sliders 53, 54, and 55 in their extreme left-hand positions. At this time terminals R. and W of motors 23, 33, and 31 will all be substantially shortcircuited, which will cause these motors to open their respective auxiliary switches so that all of the engines are out of operation.

As the space temperature rises above '15 F. the slider 45 will begin moving to the left across resistance 46 thereby causing the motor 5| t0y shift sliders 53, 54, and 55 to the right. At this time the sliders 54 and 55 will remain in engagement with the contact strips 58 and 66 and thus the motors 33 and 31 will remain stationary. However, the slider 53 will be traversing the resistance 56 and thus insert a portion of the resistance 56 into the short-circuit between terminals R and B while removing this same portion from the circuit between terminals R and W. This will cause the proportioning motor 23 to begin opening the throttle valve 2|. When the throttle valve 2| opens to the minimum position, the auxiliary switch 29 will close for placing the engine |8 into operation. Now as the space temperature continues to increase, the slider 53 will shift further to the right on resistance 58 thus operating motor 23 for opening the throttle valve 2| further for increasing the engine speed. When the space temperature increases to a point wherein the slider 53 is one-third of the way across resistance 56, the throttle valve 2| will be wide open and thus engine i8 will operate at maximum capacityl If the space temperaturecontinues to increase.

the slider 54 will begin traversing resistance 51 4 thus causing the throttle valve motor 33 to begin opening movement of throttle valve 34. Upon opening of the throttle valve 34 to its minimum position, the auxiliary switch 32 will close thus energizing the relay 3| and the ignition coil for placing the engine 38 into operation. At this time the slider will still remain in engagement with the contact strip 6l! and thus the engine 35 will continue to remain at rest. The throttle valve 34. is adjusted relative to the mercury switch 32 sothat the engine 38 when started operates at slightly above 50% capacity. When this engine starts, the mercury switch 8| connects the slider 'I6 to the wire 65 of the control circuit for the throttle valve motor 23. The

`slider 16 is therefore connected to terminal R of motor 23 and acts to place the right-hand portion of resistance 11 in circuit between terminals R and W and the left-hand portion of this resistancev between terminals R and B of motor 23. The slider 16 is adjusted so that the right-hand portion of resistance 11 is smaller than the lefthand portion. Consequently the connecting of slider 16 to terminal R of motor 23 due to starting of engine 30, reduces the amount of resistance between terminals R and W as compared to the resistance between terminals R and B. This causes operation of the proportioning motor 23 to a position wherein the throttle valve 2| limits the engine speed' to slightly over half capacity. It will be apparent that by adjusting the slider 'I6 the speed of the engine I8 may be reduced to approximately the same speed that engine 30 is now operating.

It will now be apparent that as the cooling load increases from zero to one-third load, the engine I8 will be started and its speed graduatingly increased to a maximum. When the cooling load rises above one-third full load, the engine 30 is placed into operation at approximately one-half capacity and the speed of engine |8 is simultaneously reduced so that the two engines operate at the same speed and slightly over onehalf capacity.

Upon continued increase in cooling load, the sliders 53 and 54 will traverse the resistances 56 and 51 for increasing the speeds of engines I8 and 30 simultaneously until both engines are operating at full speed. If the space temperature still continues to increase, the slider 55 will begin traversing resistance 59 which will cause the proportioning motor 31 to close its auxiliary switch 39 for thus energizing relay 38 and the ignition coil to start the engine 3.5. The throttle valve 36 and auxiliary switch 39 are adjusted so that the switch 39 closes when the throttle valve 36 is positioned for causing the engine 35 to operate at slightly over two-thirds capacity. When this engine starts, it causes the mercury switches 93 and 98 of the manifold pressure responsive device 94 to close which respectively connect the potentiometers 81 and 99 into the control circuits of throttle valve motors 23 and 33. The connecting of potentiometer 81 into the control circuit of motor 23 causes this motor to close the throttle valve to a position causing operation of the engine I8 at slightly over two-thirds capacity in a manner'which will now be apparent. Also the connecting of potentiometer 99 into the control circuit of motor 33 causes this engine to be slowed down from full speed to reduce its capacity to slightly over two-thirds. Therefore all three engines will now be operating at slightly over two-thirds capacity which provides slightly more capacity than can be obtained by operating two engines at full speed. Upon continued rise in space temperature it will be apparent that the three engines will be speeded up simultaneously so that when the space temperature rises to F. all threeengines lwill be 'operating at full speed. Upon a'fall in space temperature it will be apparent that the operation as described above will take place in reverse order. Thus .the speeds of the engines will be reduced to approximately two-thirds capacity at which time the engine 35 is placed out of operation and the engines I8 and 30 are increased in speed to operate at full capacity. Then upon further temperature drop the speeds of engines I8 and 30 are decreased until the two engines are operating at approximately 50% capacity. At this l time the engine 30 will be stopped and the engine |8 speeded up to operate at full capacity. Then upon continued temperature drop this engine will be slowed down until finally it is placed out of operation entirely.

Figure 2 Referring to Figure 2, this figure shows a modied control arrangement. In this figure the compressors 20|, 202, and 203 are connected to a common discharge line 204 which is connected to a condenser 205 having a liquid line 206 leading to the cooling coil 201 -located within the air conditioning chamber 208. The outlet of this coil is connected to the suction line 209 which is connected in turn to the intake of each compressor. These compressors are driven respectively by means of internal combustion engines 2| 0, 2|I, and 2|2 having automatic starting relays 2|3, 2|4, and 2|5 respectively, these engines also having ignition coils connected so as to be energized with the starting relays. The engines 2I0, 2| I, and 2|2 are also provided with throttle valves 2|6, 2|1, and 2|8 which are positioned by proportioning motors 2| 9, 220, and 22| respectively. V

Connected to the suction line 209 by means of a tube 222 is a suction pressure controller generally indicated as 223. This controller may include a bellows 224 which actuates a bell crank lever having an actuating arm or slider 225 cooperating with a resistance 226. .It will be apparent that if the suction pressure increases, the bellows 224 will expand against the action of spring 221 thereby causing movement of the slider 225 to the left across resistance 226. Upon decrease in suction pressure the bellows 224 will contract for causing movement of the slider 225 to the right.

Also controlling the throttle valve motor 2|9 is a two-position type return air thermostat 230. This thermostat may include a bellows 23| connected by a capillary tube 232 to a control bulb 233 which is located in the return air duct leading to the chamber 208. This bellows 23| actuates a switch carrier 234 carrying a double electrode type mercury switch 235. When the return air temperature rises above a predetermined value such as 75 F. the bellows 23| will expand 5 suiciently against the action of a biasing spring 236 for bridging the left-hand electrodes of mercury switch 235. However, when the return air temperature is below this value the bellows 23| will be contracted thereby causing the righthand electrodes of switch 235 to be closed.

It will be noted that terminal R of throttle valve motor 2|9 is connected by wire 231 to the common terminal of mercury switch 235 and the left-hand terminal of this switch is connected by wire 238l to the slider 225 of the suction pressure controller 223. The right-hand end of resistance 226 is connected by wires 239 and 240 to terminal W of motor 2|9, while the left-hand end of resistance 226 is connected by Wire 24| to terminal B. Therefore when the space temperature is above 75 F. which causes the left-hand electrodes of mercury switch 235 to be bridged,

controller acts to control motor I9 in a manner to open the throttle valve 2|6 as the suction pressure increases while closing this throttle valve after the suction pressure decreases. However, when the space temperature falls below 75 F., the left-hand electrodes of mercury switch 235 will be unhridged for disconnecting the suction pressure controller 223 from the control circuit of motor 2|9. At this same time the right-hand electrodes of mercury switch 235 will be bridged which will complete a circuit from terminal R through wire` 231, Y switch 235, wire 292, and wire 249 to terminal -W of motor 2|9 which will cause this motor to completely close the throttle valvel6. y

The throttle valve motor 2|9 is provided with an operating shaft 243 which lcarries cams 244 and 245 and a -slider 246 which cooperates with a resistance 241. The slider 246 is connected by wire 248 to terminal R of the throttle valve motor 229 while the resistance 241 is connected to terminals B and W by wires 249 and 259. It will be apparent that the potentiometer formed of slider 246 and resistance 241 acts to control the position of Vthe throttle valve motor 229 in accordance with the position of the motor 2|9. This arrangement provides for controlling the motors 2|9 and 229 in unison by a single suction pressure controller 223. The motor 229 is provided with an operating shaft 25| which actuates cams 252 and 253 and also actuatesV the slider of\ a potentiometer 254 which is connected to the throttle valve motor 22| by wires 255, 256, and 251. The suction pressure controller 223 therefore controls the throttle valve motors 2|9, 229 and 22| in unison.

Referring again to the throttle valve motor 2|9, the cam 244 actuates a switch 258 while the cam 245 actuates a switch 259. The cam 244 is adjusted upon the operating shaft 243 so that the switch' 258 remains open until the'throttle 'valve 2|6 is opened to a point corresponding to 25% capacity 'of engine '2|9, The cam 245 is adjusted so as to maintain the switch 259 closed -so long as'the throttle Valve 2|6 is adjusted for more than engine capacity. Y

The switches 258 and 259 control a relay generally indicated as 269, this relay b'eing indicated as in a housing with transformer 26|. The relay 269 is of usual form consisting of a pull-in coil 262 which actuates through a suitable armature the switch arms 263 and 264 cooperating with contacts 265 and 266 respectively. When pull-,in coll 262 is energized,`the switch arms 263 and 264 engage their respective contacts while when this coil is deenergized the switch arms are disengaged from their contacts by the action of gravity or springs, notshown.

The cams 252 and 253 of the throttle valve motor 229 control switches 219 and 21| respectively. The cam 252 is adjusted on shaft 25| so as to close the switch 219 when the throttle valve motor 229 is `positioned corresponding to 98% of engine capacity. The cam 253 is adjusted so as to maintain the switch 21| closed so long as the throttle valve 2|1 is opened beyond a point corresponding to 45% engine switches 219 and 21| control a relay 212 which is associated with a transformer 213. The relay 212 is also in part controlled:l by means of a thermo-electric timer 214 which may consist of a bimetallic element 215 carrying a contact ,which cooperates with a contact 216. This timer y .`also includes a heating element 211 for influencing the bimetallic element 215.

right-hand electrodes of` capacity.` The an operating shaft 289 carrying cams 28| and tively. The cam 29| is adjusted so as to close switch 283 only when the throttle valve motor 22| opens the throttle valve 2|8 wide open. The cam 292 is adjusted so as to maintain the switch 284 closed so long as the throttle valve 2|8 is open beyond 62% capacity position. The switches 283 and 284 control a relay 285 which is the same as relay 212. This relay 285 is also in part controlled by a thermo-electric timer 286 having a bimetallic element 281 cooperating with contact 288 and also having a heating element 289. The various circuit connections will be described in the following statement of operation.

Operation of Figure 2 Assuming that the space temperature con' troller 239 is in the position shown for placing the suction pressure controller 223 in control of the ,throttle valve motors 2|9, 229, and 22|; for a relatively. low value of suction pressure this controller will cause the throttle valves 2|6, 2|1, and 2|8 to be substantially closed. When the suction pressure rises to a point suiiicient to cause closing of the switch 258 of motor 2|9, the relay 269 will be energized as follows: transformer secondary 299, wire 29|, switch 259, wire 292, switch 258, wire 293, pull-in coil 252, and wire 294 to secondary 299. Engagement of the switch arm 264 with contact 266 will complete the energizing circuit through wires 295 and 296 for the relay 2-|3 and the ignition coil, thus placing the engine 2|9 into operation. Engagement of the switch arm 263 with contact 265 will complete a holding circuit for coil 262 as follows: transformer secondary 299, wire 29|, switch 259, wire 292, wire 291, contact 265, switch arm 263, wire 298, coil 262 and wire 294 to secondary 299. Thus the relay 269 will be maintained energized independently of the switch 252 and this relay 4vwill remain energized until the throttle valve 2 I6 is closed to a point where the switch 259 is opened. The switch 258 is thus a switch for starting the engine and the switch 259 is a switch for stopping the engine.

As the load on the system increases, the suction pressure will rise which will cause the suction pressure controller 223 to operate motors 2 I9, 229, and 22| in-the direction for opening the throttle valves 2| 6, 2|1, and 2|8. However, at this time the relays 212 and 285 and the ignition coils for engines 2| and 2|2 will not be energized and consequently these engines will not be in question. Therefore as the load rst begins increasing, only the engine 2|9 will be in operation and the speed of this engine will be increased progressively as the load increases.

When the load upon the system becomes such that the value of suction pressure causes the suction pressure controller 223 to open the throttle valves beyond 98% capacity positions, the switch 219 of the throttle valve motor 229 will close thus energizing the relay 212 as follows: transformer secondary 399, wires 39| and 392, switch 219, wire 393, pull-in coil 394, and wire 395 to secondary 399. This will cause the switch arms 396 and 391 to engage their respective contacts. Engagement of the switch arm 391 with its contact will complete an energizing circuit for theA starting relay 2 |'4 and the corresponding ignition coil through wires 398 and 399 thereby vus plete a maintaining circuit for the pull-in coil 304 through switch 21| as follows: secondary 300, wire 30|, wire 3|0, switch arm 306, wire 3||, Switch. 21|, wires 3|2, 3|3, and 303, coil 306 and wire 305 to secondary 300. Consequently the 4relay 212 will remain'energized for maintaining gin closing the throttle valves 2|6, 2|1, and 2|8.

. The engines 2|0 and 2|| will therefore begin to and wire 305 to secondary 300. Consequently slow up and'in fact will slow up until the suction pressure stops falling. At this time the capacity of the engines will just exactly balance the cooling load upon the system.

electric timer 214 is provided. This timer is ar- -ranged so that as long as the bimetallic element 215 is cold, it engages contact 216 and thus provides a maintaining circuit for the coil 304 which is independent of switch 21| as follows: transformer secondary 300, wire 30|, wire 3| 0, switch arm 306, wires.3l|, 3|5, and 3|6, bimetallic element 215, contact 216,:wire 3|3, wire 303, coil 304 during the initial surges produced when the engine 2| ilrst starts, this engine is locked in'operation by the timer 214. During this time, the heating element 211 of the timer 214 is energized by a circuit through the switch arm 306 as follows: transformer secondary 300, wire 30|, wire 3|0, -switch arm 306, wires 3| I, 3|5, and 3|1, heating element 211, and wires 3|8 and 305 to secondary 300. This .energization of heating element 211 will after a predetermined period cause the bimetallic element to disengage from contact 216 and thus render the switch 21| operative to stop the engine 2| when the throttle valve 2|1 is closed to a point where this switch is opened.

As the load continues to increase, the suction pressure will rise for causing the throttle valves 2|6, 2|1, and 2|8 to open simultaneously for increasing the speeds of engines 2|0 and 2||.

so that they are all open approximately equally so that the two engines operate at equal speeds, the `speeds being increased simultaneously upon increase in suction pressure. When the' suction pressure rises to a point wherein all three throttle valves are wide open the switch 203 of the throttle valve motor will close thereby energizing the relay 285 which in turn energizes the starting relay 2|5 and corresponding ignition coil for placing engine 2|2 in operation. All three engines will therefore now be operating at full speed and consequently the suction pressure will begin to fall. At this timethe thermo-electric timer 286 will short-circuit the switch 286 and thus pre- It will be noted that the throttle valves are adjusted agences vent any surges in suction pressure which occur upon starting of engine 2|2 from stopping this engine. Due to the falling suction pressure, the engines will be simultaneously slowed down until the suction pressure stops falling, which will oc'cur when each engine is operating at substantially two-thirds capacity. Upon continued increase in cooling load the suction pressures will begin increasing thereby causing the engines to be speeded up simultaneously for carrying the increased load.

Upon falling cooling load from this point, the engines will be slowed clown simultaneously until a point is reached at which all three engines are operating at substantially 62% capacity.4 Upon further decrease in load the switch 286 of throttle valve motor 22| will open thereby placing the engine 2|2 out of operation. Due to the placing of engine 2|2 out of operation the suction pressure will gradually increase thus vcausing Vthe suction pressure controller 223 to begin opening the throttle valves for speeding up engines 2|0 and 2| until the increased speed prevents further rise in suction pressure. Thus now only two engines will be operating but at higher speed in order to carry the load. Upon further fall in cooling load, the suction pressure will continue to decrease which will cause the throttle valves to be graduatingly closed for thereby decreasing the speeds of engines 2|0 and 2| When the cooling load falls to a point at which both engines are operating only at 45% capacity, the switch 21| of throttle valve motor 220 willopen for placing the engine 2I| out of operation. As a result the ysuction pressure will once more begin rising which will cause the speed of engine 2|0 to be increased until the rise in suction pressure is arrested. 'Ihen upon further decrease in load the suction pressure will once more begin decreasing for slowing down the engine 2|0 and when this engine is slowed down to its minimum desired rate of operation the switch 259 will open for stopping this engine. Y

-It will be understood that whenever the space temperature is below the setting of the return air thermostat all of the engines are placed out of operation irrespective of the value of suction pressure.

In the foregoing description, it has been assumed that the engines described are gasoline engines, and that the throttle valves are associated with the usual carburetors. If the invention is applied to gas engines, it will be understood that suitable valves may be provided in the gas lines in advance of the throttle valves for shutting o :the flow of gas when the corresponding engine is not inoperation. It will also be understood that the engines may be provided with suitable automatic choking devices for obtaining proper starting action.

From the foregoing it will be apparent that this invention providing a control arrangement for multiple compressor refrigeration u nits wherein the compressors are driven at variable speeds in accordance with the cooling load and in which the number of engines in operation is also varied in accordance with )the cooling load. Also it will be apparent that irrespective of the number of engines in operation, all of the engines in operation will operate` at equal speeds, this result being achieved by slowing down the engines already in operation whenever another engine is placed into operation. While I have shown only two embodiments of this invention, it will be apparent that the inventionmay take various other and pressure and capacities have been mentioned,

it will be understood that these values are illustrative only. As .the invention may take various forms and be applied to various applications, I

.desire to be limited only by the scope of the appended claims. -f

I claim as my invention:

1. In a system of the class described, in combination, a plurality of load devices adapted to be ldriven at variable speed, the speed of each load device being indicative of the load which said device is carrying, an internal combustion engine for each of said load devices for driving the same, means responsive to the load on the system for varying the speed of one of said engines from a predetermined minimum to a maximum, means actuated upon the load on the system rising above the capacity of said one engine for starting another of said engines, and means for causing said engines to operate at substantially equal speeds after starting of said other engine.

2. In a system of fthe class described, in combination, a pluralityof load devices adapted to be driven at variable speed, the speed of each load device being indicative of the load which said device is carrying, an internal combustion engine for each of said load devices for driving the same, means responsive to the load on the system for varying the speed of one of said engines from a predetermined minimum to a maximum, means actuated upon the load on the system rising above the capacity of said one engine for starting anorther of said engines, and means actuated upon starting of 'said other engine for slowing down said one engine an amount sufficient to cause said engines to operate at substantially equal l speeds.

3. In a system of the class described, in combination, a plurality of load devices adapted to be driven at variable speed, the speed of each load device being indicative of the load which said device is carrying, an internal combustion engine for each of said load devices for driving the same, a speed controller for each of said engines, individual motor means for actuating each of said speed controllers, control means responsive to a condition indicative of the load on the system for controlling said speed controllers in a manner to operate said engines at substantially equal speeds and to increase fthe` engine speeds upon increase in load, and means for'sequentially placing said engines into and out of operation.

4. In a system of the class described, in combination, a plurality of load devices adapted to be driven at variable speed, the speed of each load device being indicative of the load which said device is carrying, an internal combustion engine for each of said load devices for driving the same, a speed controller for each of said engines, individual motor means for actuating each of said speed controllers, control means responsive to a condition indicative of the load on the system for controlling said speedfcontrollers in a, manner rto operate said .engines at 'substantially equal speeds and to ,increase the engine speeds upon increase in load, and means operated by said moto:` means for placingcorresponding engines into and out of operation sequentially.

5. In a. system of the class described, in combination, a plurality of load devices adapted to be driven at variable speed. the speed of each load device being indicative of the load which said device is carrying, an internal combustion engine for each of said load devices for driving the same, means for sequentially placing said engines into and out of operation, a speed controller for each engine, motor means for actuating said speed controllers, and control means responsive to a condition indicative of the load on the system for' controlling said motor means and hence said speed controllers in a manner to operate said engines at substantially equal speeds and to increase the engine speeds upon increase in load, saidl control means including means responsive to the number of engines in operation for adjusting the speed maintained by at least one of said engines.

6. In a system of the class described, in combination, a plurality of load devices adapted to be driven at variable speed, the speed of each load device being indicative of the load which saiddevice is carrying, an internal combustion engine for each of said load devices for driving the same, a speed controller for each of said engines, individual motor means for actuating each of said speed controllers, control means responsive to a condition indicative of the load on the system for controlling said speed controllers in a manner to operate said engines at substantially equal speeds and to increase the engine speeds upon increase in load, said control means including a condition responsive device, a motor controlled thereby, a

plurality of controllers actuated by said motor for controlling said speed controller motor means, and means for adjusting said controllers in accordance with the number of engines in operation.

'7. In a system of the class described, in combination, a plurality of load devices adapted to be driven at variable speed, the speed of each load device being indicative of the load which said device is carrying, an internal combustion engine for each of said load devices for driving the same, a speed controller for each of said engines, individual motor means for actuating each of said speed controllers, means actuated by said individual motor means for placing said engines into and out of operation, control means responsive to a condition indicative of the load on the system for controlling said motor means and, hence said speed controllers in a manner to operate said engines at substantially equal speeds and to increase the engine speeds upon increase in load, said control means including means responsive to the number of engines in operation for adjusting the speed maintained by at least one of said engines.

8. In a system of the class described, a iirst internal combustion engine, a second internal combustion engine, both of said 'engines being adapted to operate art variable speed and being connected to a common load, load responsive means for graduatingly increasing the speed of one of said engines from a minimum to a maximum to increase the load which said one engine carries as the load on the system increases, means for starting the other of said engines when the load increases to a value which is more than desirable for said one engine to carry, means actuated when said one engine is started for reducing the speed of said other engine to a value wherein both engines operate at substantially equal speeds and therefore carry substantially equal loads, and means for incre the speed of said one engine as the load continues to increase, said last mentioned means being arranged to increase the speed of said other engine proportionately to the increase in speed of said one engine.

9. In a. system of the class described, in combination, a plurality of load devices adapted to be driven at variable speed, the speed of each load device being indicative of the load which said device is carrying, an internal 'combustin engine or each of'said load devices for driving the same, a speed controller for each of said engines, individual motor means for actuating each of said speed controllers, control means responsive to a condition indicative or the load on the system for controlling said speed controllers .in a manner to operate said engines at substantially equal speeds and lto increase the engine speeds upon increase in load, said control means comprising a load condition responsive controller for controlling one of said motor means andY a controller actuated by said one motor means for controlling another of said motor means, and means for sequentially placing said engines into and out of,

operation. Y

10, In a system of the class described, in combination, a plurality of load devices adapted to be driven at variable speed, the speed of each loadl device being indicative of the 1aed which said device is carrying, an internal combustion engine for each of said load devices for driving the same, a speed controller for each of said engines, individual motor means for actuating each of said speed controllers, control means responsive to a condition indicative of the load on the system for controlling said speed controllers in a manner to operate said engines at substantially equal speeds and to increase the engine speeds upon increase in load, said control means/'comprising a load condition responsive controller for controlling one of said motor means and a controller actuated by said one motor means for controlling another oi said motor means, and means also actuated by said motor means for placing corresponding engines into and out of operation sequentially. y

11. In a'system of the class described, in combination, a plurality of load devices adapted to be driven at variable speeds, the speed of each 'l load device being indicative of the load which Ilsaid device is carrying, said devices being connected to a common load, an internal combustion engine for each-of said load devices for driving the same, a speed controller for each engine, ,means responsive to a condition varying in ac- I cordance with the relationship between the engine output and the load-on the system for controlling said speed controllers in a manner tending to increase the speeds of the engines simul- 'taneously when the change in the condition in- `i dicates that the load is increasing above the output of the engines while decreasing the speed `of said engine whenithe change in said condition indicates that the load is decreasing below the output of the engines, said speed controllers be-v engine for each of said load devices for driving (the same,- a speed controller for each engine, means responsive 'to a, condition varying in accordance with the relationship between the engine output and the load on the system for controlling said speed controllers in a manner tending to increase the speeds ofY the engines simultaneously when the change in the condition indicates that the load is increasing above the output of the engines while decreasing the speeds of said engine when the change in said condition indicates that the load is decreasing below the output of the engines, said speed controllers being adjusted for operating said engines at substantially equal speeds, a controller for each engine for starting and stopping the same, and means controlled by said condition responsiveV means for controlling said starting and stopping means sequentially in a manner to sequentially place said engines in operation upon increase in load while sequentially placing said engine out of operation upon decrease in load. N

13. In a system of the class described, in combination, a pair of load devices adapted to be driven at variable speeds, the speed of each load device is carrying, said load devices being con nected -to a common load, an internal combustion engine for each of said load devices for driving the same, a. speed controller for each engine, means responsive to a. condition varying in accordance with the engine output and the load on the system 'for controlling said speed controllers in a manner tending to increase the speeds of the engine simultaneously when the change in the condition indicates that the output is below the actual load while decreasing the engine speeds when the change in said condition indicates that the output is below the actual load while decreasing the engine speeds when the change in said condition indicates that the output is above the actual load, a. controller for one of said engines for starting the same, said controllerV being controlled by said condition responsive means and operating to startthe engine when said condition reaches a predetermined value, and a control-ler for said one engine for stopping the same, said last mentioned controller being controlled by said condition responsive means in a. manner to stop said one engine when said condition falls to a predetermined value which is lower than said iirst mentioned value.

14. In a system of the class described, in combination, a pair of load devices adapted to be driven at variable speeds, said load devices being connected to a. common load, an internal. combustion engine for each of said load devices fori driving the same, a speed controller for each engine, means responsive to a condition varying in accordance withthe engine output and the load on the system for controlling said speed controllers in a. manner tending to increase the speeds of the engines simultaneously when the change inthe condition indicates that the output is below the actual load while decreasing the engine speeds when the change in said condition indicates that the output is above .the actual load, a controller for one of said engines for starting the same, said controller being controlled by said condition responsive means and operating .to start the engine when said condition reaches a predetermined value, a controller for said one engine for stopping the same, said last mentioned controller being controlled by said condition responsive means in a. manner to stop said one engine when said condition falls a predetermined value which is lower than said rst mentioned value, and timing means for rendering said last mentioned controller inoperative to stop said one engine for a period following starting thereof to therebyr prevent stopping of said engine due to surges in. said condition caused by' starting of said one engine. Y

`driving the same, a speed controller for each.

engine, means responsive Ito a. condition varying in accordance with -the engine output and the load on the system for controlling said speed controllers in a manner tending to increase the speeds of the engines simultaneously when the change in the condition indicates that the output is below the actual load while decreasing the engine speeds when the change in said condition indicates that the output is above the actual load,

control means responsive to said condition for,

starting and stopping one of said engines, and means for preventing said control means from stopping said engine until a. timed period following starting of said engine. Y

16. In a system of the class described, in combination, a load device, an internal combustion engine for driving said load device at variable speed, means responsive to a condition varying in accordance with theV engine output and the load on the system for increasing the speed -of said engine when the change in said condition indicates that the engine output is smaller thanthe actual load upon' the system and for decreasing the speed of the engine when the change in said condition indicates that the engine output is greater than the actual load, means for starting and stopping said engine also controlled in accordance with said condition, and timing means for preventing said last mentionedrmeans from stopping said engine for a timed period following starting of said engine.

17. Ina system of the class described, in combination, a load device, an internal combustion engine for driving said load device Yat variable speed, a speed controller for said engine, load responsive means for controlling saidvspeed controller in a manner to vary the engine Speed in accordance with the load on the system, control means for starting and stopping said engine, means responsive to a condition Avarying as a resultant of the engine output and the actual load on the system for controlling said control means, and timing means for preventing said control means from stopping the until a timed period following st of the engine.

18. In an air conditioning system, in combination, refrigeration system means for cooling the air and including a plurality of compressors, an internal combustion engine for each of said compressors fordriving the same, means responsive to the load on the system for varying the speed of one of said engines from a predetermined minimum to a maximum, means actuated upon the load on the system rising above the capacity of said one engine for starting another of said engines, and means for causing said engines to operate at substantially equal speeds after starting of said other engine. y

19. In an air conditioning system, in combination, refrigeration system means for cooling the air and including a plurality of compressors, an internal combustion-engine for each compressor for driving the same, a speed control means for each engine, means responsive to a condition of the air in said space which is affected by the operation of said compressors for controlling said Aspeed control means in a manner to actuate said speed controllers in sequence, means for starting and stopping one of said engines. and means actuated with starting of said one engine for adjusting the speed control means of another of said engines in a manner to reduce the speed thereof.

20. In conditioning system, in combination, refrigeration system means for cooling the air and including a plurality of compressors connected to a common suction line, an internal combustion enginefor each compressor for driving the same, a speed controller for each engine, means responsive to suction pressure for actuating said speed controllers simultaneously in a manner to increase the speeds of said engines 'upon increase in suction pressure and to decrease the speeds of said engines upon decrease in suction pressure, said speed controllers being arranged so as to cause operation of said-compressors at substantially equal speeds, and means actuated with said speed controllers for starting and stopping one of said engines.

2l. In a system of the class described, in com- Ibinatican, a plurality of load devices adapted to be driven at variable capacities, a variable speed prime mover for each of said load devices for driving the same, the capacity of each load device being dependent upon its speed, means responsive to the load on the systems for varying the capacity of one of said prime movers from a predetermined minimum to a maximum, means actuated when the load on the system rises above the capacity of said one prime mover for starting another of said prime movers, and means actuated upon starting of said other prime mover for reducing the capacity of said one prime mover an amount sufficient to cause said prime movers to operate at substantially equal capacities.

, JOHN L. HARRIS. 

